1. Field of the Invention
The present invention relates to conductor assemblies and methods of forming both wiring assemblies and systems incorporating conductor assemblies which, when conducting current, generate a magnetic field or which, in the presence of a magnetic field, induce a voltage. Such wiring, or conductor, assemblies may be components used in systems that rely on the generation of large and uniform magnetic fields.
2. Background Art
It is of continued importance across many sectors of the world economy (e.g., research and development, medical applications, rotating machines, and the like) to achieve improved performance in magnetic conductor assemblies. Development of new and improved commercial applications is dependent on an ability to create large and uniform magnetic fields. Advancements are also needed in numerous performance and reliability factors to realize commercially useful embodiments in medical, industrial and commercial applications. For example, it is desirable to make charged particle therapy cancer treatment (e.g., proton and carbon therapy) more available to patients, but these systems require cyclotrons that utilize very large magnets to steer beams of high energy charged particles. System size and cost severely limit the availability of these applications. Currently, the gantries used for proton therapy treatment rooms may extend multiple stories in height and weight over one hundred tons. One impediment to further deployment of these and other charged particle beam systems is the size and cost of the beam acceleration and focusing equipment.
Numerous magnet applications require provision of a magnetic field on the inside or the outside of a cylindrical structure with a varied number of magnetic poles. Examples of such applications are use of magnets for charged particle beam optics such as used in particle accelerator applications, particle storage rings, beam lines for the transport of charged particle beams from one location to another, and spectrometers to spread charged particle beams in accord with particle mass. Magnets of various multipole orders are needed for charged particle beam optics. In such charged particle beam applications dipole magnets are needed for steering the particle beam, quadrupoles are needed for focusing the beam, and higher order multipole magnets provide the optical equivalent of chromatic corrections.
Field errors (i.e., deviations from the ideal field strength distribution for a given application) in such systems are known to degrade the performance of the beam optics, leading to a rapid increase in beam cross sections, or beam loss within the system. Analogous to light optical systems, for which the lenses conform to predefined geometries and are ground accordingly with very high precision to render satisfactory resolution of the transmitted image, optimal performance of magnets in charged particle beam systems is dependent on creation of optimal positioning of conductor in winding configurations. This includes achievement of mechanical tolerances which result in very close conformity of the fabricated systems with predefined configurations to achieve necessary field uniformity. This is recognized for a variety of magnet designs, including double helix magnets and saddle coil magnets. See, for example, the following patent applications, each now incorporated herein by reference: U.S. 2009/0251257 filed Apr. 2, 2008, U.S. Pat. No. 7,992,884 filed Jun. 5, 2008 and PCT/US 2013/73749.
Numerous winding configurations for single-helix, double-helix, saddle coil and other conductor configurations can be manufactured by machining grooves into composite or metallic support structures, into which a conductor is inserted and, as needed, bonded into place with appropriate adhesives. The machined grooves precisely define the conductor layout of the winding and simultaneously stabilize the conductor mechanically to counteract Lorentz forces that act within the coil windings. Winding configurations of the types mentioned above, as well as the embodiments disclosed herein, typically surround a cylindrical aperture, with the conductor inserted into machined grooves to follow a 3-dimensional space curve.
The current-carrying conductor configurations used for charged particle beam optics are typically of cylindrical shape, with the conductors surrounding a tube, also of cylindrical shape. During operation, the tube is evacuated and a particle beam of narrow width passes along the central axis of the tube. The field-generating winding configurations for such applications, in most cases, consist of multiple saddle shaped layers of winding. Each layer comprises multiple turns of winding as shown in FIGS. 1A and 1B of PCT/US 2013/73749 (the '749 application), and the shape of the saddle coil winding closely matches the shape of the cylindrical beam tube. Except as disclosed in the '749 application, such saddle-shaped winding configurations for generating magnetic fields with a given pole number have typically been produced by winding the conductor over itself and around a central island. In an embodiment, the present invention contemplates a saddle coil conductor configuration and placement of the conductor in grooves as described in the '749 application.
The present invention is based, in part, on recognition that definition of the conductor configuration in, for example, a saddle coil magnet (i.e., the conductor path) and accuracy of conductor placement in the winding configuration are critical to acquiring satisfactory or optimal field uniformity, especially in the case of large magnets (e.g., magnets having lengths on the order of about 15 m) and in the case of superconducting windings. With recognition that numerous applications of magnetic fields, in addition to those related to charged particle beam optics, have potential for improved performance based on improved field uniformity, practical limitations in conventional fabrication processes may adversely affect field uniformity or limit magnet size. Field uniformity may be compromised by limitations in the fabrication process when the required magnetic coils are several meters long, as is often required for coil structures. Examples of magnets requiring large coil lengths are the bending magnets used in large accelerators like the Large Hadron Collider (LHC) near Geneva, which includes magnets having lengths of about 15 m. However, due to superior winding support and field quality achievable with machined grooves, such coil configurations of the types disclosed in the '749 application are best suited for future high field accelerator magnets having field strengths on the order of 16 to 20 Tesla.
The present invention provides a method of manufacturing and assembling segmented support structures for conductor assemblies and magnets, including magnets comprising coil windings which are multiple meters in length. The support structure into which the machined grooves are formed to define the conductor path may consist of a composite material or may be a metal in the shape of a cylinder, but which need not be manufactured in the form of a single piece of stock. Rather, the support structure may be formed in multiple connectable support structure segments. The plurality of segments includes multiple individual segments, each of sufficient length to support multiple individual coil turns in a helical or other desired conductor configuration. When the segments are connected, a contiguous desired conductor configuration, which may, for example, be helical, is formed and continues without interruption from connectable segment to connectable segment.
In the long term, for charged particle therapy and certain other high magnetic field applications, it is likely that superconducting magnets will be preferred over resistive magnets. Generally, superconducting magnets offer very stable and high field strengths and can be substantially smaller in size than resistive magnets. Moreover, the power demands of superconducting magnets are very low. However, the opportunity to provide superconducting magnets in new applications may be compromised because of the well-known quenching phenomenon. When the superconducting material undergoes an unexpected and rapid transition to a normal, non-superconducting state this can result in rapid formation of a high temperature hot spot which can destroy a magnet. Designs which improve reliability have been costly. Cost is a major constraint to greater commercialization of conventional superconducting magnet technologies which rely on saddle or racetrack coils. Moreover, for a given set of operating conditions, significant design efforts must be employed to achieve requirements of field uniformity and to assure that quenching does not occur during normal system use.
Whether future systems employ resistive or superconductive windings, a need will remain to improve design efficiency, reliability and field quality. In order to deploy carbon-based systems for charged particle cancer treatment, for example, the use of superconducting magnets may be imperative in order to meet the bending requirements of the high energy carbon beam. Coil segments used to bend beams are very complex to manufacture and must be very stable in order to implement a curved trajectory. Further, it is very difficult to apply conventional geometries, e.g., saddle coil and race track configurations, to curvilinear applications in an easily manufacturable manner and still meet requirements for field configurations.
Thus there exists a need for an easily manufacturable conductor assembly to be utilized in magnetics applications, that will support the manufacture and assembly of any winding or conductor configuration.